The long term goal of this project is concerned with the neural organization and integration of sensory information used by the nervous system to generate motor commands. The specific aims focus on the organization and representation of sensory information in spinal circuits that project to the cerebellum, to areas involved in the control of posture and locomotion. The dorsal spinocerebellar tract (DSCT) neurons receive sensory information from sensory receptors in the limbs and they convey the results of the spinal processing of this information directly to the spinocerebellum. Although the project is focussed on the spinal cord and its relationship to the cerebellum, it nevertheless addresses central issues about neural processing involved in sensorimotor integration. An underlying perspective guiding this work is that communication among brain areas occurs within common frames of reference. In fact, the relationships found between neural activity and limb kinematics in spinal circuits projecting to the cerebellum resemble in many ways those seen in other brain areas involved in motor behavior. This project will use single neuron recording techniques and multivariate regression analysis to relate neural activity to limb kinematics during passive stepping and self-initiated locomotion in the cat. The results will be used to test specific hypotheses about the spinal and cerebellar organization of sensorimotor systems involved in the control of locomotion. The significance of understanding how these systems are organized is in the potential insight they offer into the workings of the motor control system. Motor disorders account for a large fraction of the disabilities leading to lost productivity or decreased quality of life in this country. A better understanding of the normal function of the motor control system can be expected to lead to improved therapies and rehabilitation strategies even if it does not lead immediately to "cures".